The incidences documented are of five taxonomic groups: pathogens, phytoplankton, algae and plants, invertebrates, and fish, recorded in coastal, marine, and brackish areas. For each group, information is organized by region, primarily the northeast and northwest Atlantic, Baltic, and Mediterranean. This is intended to provide insight into the species' distribution and dispersal. Several species of algae, crustaceans, and molluscs were the most problematic. Taxonomic identification, particularly of small organisms, remains challenging, but is critical in identifying and thus managing these species.

The intentional or accidental introduction of non-indigenous marine species can have serious ecological and economic impacts, contributing to the global loss of biodiversity, negatively affecting coastal communities, and potentially impacting on human health.